This script uses ffmpeg to convert video to vpx9 and audio to vorbis, then sox to normalize audio, and finally ffmpeg to bundle the streams back together

convert-to-vp9-ogg-webm-and-normalize-audio.sh

#!/bin/zsh
# Install needed tools:
# brew install sox --with-libvorbis
# brew install ffmpeg --with-libvpx --with-libvorbis --with-opus --with-faac
set -e
FILENAME=$1
echo "Converting $FILENAME to webm + ogg with normalized audio"

ffmpeg -i ${FILENAME} -c:a libvorbis -vn ${FILENAME}_audio_orig.ogg
ffmpeg -i ${FILENAME} -c:v libvpx-vp9 -crf 50 -b:v 0 -vf scale=840:-1 -g 50 -an ${FILENAME}_video_orig.webm
sox --norm ${FILENAME}_audio_orig.ogg ${FILENAME}_audio_norm.ogg
ffmpeg -i ${FILENAME}_video_orig.webm -i ${FILENAME}_audio_norm.ogg -c copy ${FILENAME}_normalized_full.webm
rm ${FILENAME}_audio_orig.ogg ${FILENAME}_video_orig.webm ${FILENAME}_audio_norm.ogg

# The ISC License
# Copyright (c) 2015, Heikki Rauhala

# Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.